[SOUND] Welcome back. Let's continue our introduction of this topic called lactation biology. And before we start getting into any of the kind of details and other background, it's really important that we start laying down some definitions. So I want to go through a series of definitions with you to make sure we're kind of all using the same vocabulary to talk about things. So let's go to the first set of words that we want to define. Mammogenesis, the first one that we want to talk about, is mammary gland development. So development, and we'll see when we get into the mammary development module. Mammary gland development module, it starts when the animals a fetus and runs all the way through lactation, regression, redevelopment, and so on and so forth. So there's a lot of stages that are involved in mammary gland development. So it's both really structural development particularly. Later on when we talk about functional development, we get into lactogenesis and galactopoiesis, we'll talk about those here in a second. In human area, sometimes people use the expression mammoplasia, normal or spontaneous enlargement of the breast. Normal development would be during pregnancy for example, early lactation. Spontaneous enlargement of the breast is when something else is going on. Again, we'll define some of those terms related to that in a little bit. So this is a term not normally used for a description of what's happening in animals other than humans. Certainly could be used there. Typically, we talk about mammogenesis being the more general word that encompasses all of mammary development. Lactogenesis, initiation or onset of lactation. So it's at the beginning of lactation. How does that process get started? We shift gears from structural development to functional development that processes lactogenesis. How does that happen, going from a non lactating state to a lactating state? Sometimes this word is used to indicate lactation and it really isn't. It's the initiation or onset of lactation. Again, it's a very specific kind of physiological process occurring related to that. Galactopoiesis, kind of a tongue twister sort of word. Galactopoiesis is maintenance of lactation or continuation of milk secretion. So once you get it going, once we go through this process of lactogenesis, once it's going, you somehow have to keep it going. And that's again, this process of galactopoiesis. That typically is a term where functionally the gland is lactating, so we think of that as lactation but that's not completely accurate. So these are key words mammogenesis, mammary development. Lactogensis, initiation or onset of lactation. Galactapoiesis is once you get it started you have to maintain that and keep lactation going. Let's go to the next set of words, so here a set of words that relate really to kind of the structures that are involved. Mammary glands Is a compound tubulo alveolar skin gland. It is a skin gland that's outside the body wall located in the ventral surface of the animal. Again, it's always on this part of the animal. You don't find it on the back or on the shoulders or somewhere else, it's always here. Aveolus are the basic unit of milk secretion. Milk synthesis and secretion. It's usually a single layer of epithelial cells surrounded a lumen. So they produce milk and secrete that milk into the lumen of the alveolus. Alveoli are organized in a structural unit called a lobule. So there's a bunch of these alveoli, being the plural for alveolus. Alveolus being one. Inside something that's structurally referred to as a lobule and that's kind of a functional unit. All these, typically all these alveoli within on lobule are doing the same thing and they're probably millions of lobules in a mammary gland, particularly of a cow and that sort of an animal. Breast is a term typically used to denote the human mammary gland. So, an udder is typically used to denote a complex mammary glands in ruminants and other kinds of animals. So, mammary gland is kind of the general term. Breast would be used primarily for humans, perhaps some other primates. And then udder would be used for other kinds of animals. Like cows, and pigs, and sheep, and so on and so forth. Again, if you're ever unsure mammary gland is the term which encompasses all of those. Let's go to the next slide. So here we're going to start to get into some definitions that relate to functionality of the mammary gland. So milk secretion. Milk secretion is synthesis of milk by the mammary epithelial cells, and the passage of that milk from inside the epithelial cell into the lumen of that alveolus. Synthesis in the cell and then, secretion of that out into the lumen. Now the next slide, milk removal, two components of that. One is passive removal from the cisterns. This is assuming the animal has a cistern. Cows have a cistern, these areas at the bottom of the mammary gland where milk can kind of ooze down there and collect. And we can remove that passively. On the other hand, the milk that's up in the tissue in these alveolar in the small ducts. You have to have a physical ejection called milk ejection to get that milk out. So milk removal, actually it's one thing to synthesize it. Somehow you have to get out of the gland. And again, if they have a cistern system as cows, sheep, goats and a number of other species have. You can remove some of that passively. You only get a little bit of the milk out but then you have to have this physical milk ejection, rejection of milk, milk ejection, milk let down to cause that process to get the rest of the milk out of the gland. That leads us then into milk ejection. Sometimes it's referred to as milk let down. Sometimes it's referred to as milk release. Again, it's a neuroendocrine reflex. Stimulate the mammary gland, sends nerve impulses to the brain, results in release of oxytocin from the posterior pituitary, this milk release hormone. A lot of people have heard of oxytocin, goes from the posterior pituitary, goes back by the blood to the mammary gland. Causes myoepithelial cells, which are around that alveolus to contract. Squeeze the milk. Not squeeze the milk out of the cells. Squeeze the milk out of the lumen and the small ducts and down further into the mammary gland, so it can be removed from the gland. Again, forcible squeezing of the milk from the lumen of the alveolus. So that's milk ejection. So again milk removal, gotta get the milk out to maintain lactation. Passive removal from the cisterns, physical ejection by this process called milk ejection. And then lactation then. Lactation technically is the combined processes of milk secretion. We've talked about that up here. Synthesis and then secretion out into the lumen and the small ducts. And removal of lactation, which involves again, in some species if they have a cistern the passive removal in all species, this physical ejection of milk from the alveoli and the small ducts to get out of the gland. So lactation is both of these things. It's synthesis secretion in the lumen, and then removal of the milk from the mammary gland. [SOUND]
